Making Decisions for IP Address Management (Task Map)

As part of the DHCP service setup, you determine
several aspects of the IP addresses that the server is to manage. If your
network needs more than one DHCP server, you must decide how to divide responsibility
for the addresses so you can assign some to each server. The following task
map can help you make IP address management decisions.

Task

Description

Information

Specify what addresses the server should manage

Determine how many addresses you want the DHCP server to manage,
and what those addresses are.

Number and Ranges of IP Addresses

During the initial server configuration, DHCP Manager allows you to
add one block, or range, of IP addresses under DHCP management by specifying
the total number of addresses and the first address in the block. DHCP Manager
adds a list of contiguous addresses from this information. If you have several
blocks of noncontiguous addresses, you can add the others by running DHCP
Manager's Address Wizard again, after the initial configuration.

Before you configure your IP addresses, know how many addresses are
in the initial block of addresses you want to add and the IP address of the
first address in the range.

Client Host Name Generation

The dynamic nature of DHCP means that an IP address
is not permanently associated with the host name of the system that is using
it. The DHCP management tools can generate a client name to associate with
each IP address if you select this option. The client names consist of a prefix,
or root name, plus a dash and a number assigned by the server. For example,
if the root name is charlie, the client names will be charlie-1, charlie-2, charlie-3,
and so on.

By default, generated client names begin with the name of the DHCP server
that manages them. This is useful in environments that have more than one
DHCP server because you can quickly see in the DHCP network tables which clients
any given DHCP server manages. However, you can change the root name to any
name you choose.

Before you configure your IP addresses, decide if you want the management
tools to generate client names, and if so, what root name to use for the names.

The generated client names can be mapped to IP addresses in /etc/inet/hosts, DNS, or NIS+ if you specify this at configuration.
See Client Host Name Registration for more information.

Default Client Configuration Macros

In Solaris DHCP, a macro is a collection of network configuration
options and their assigned values. The DHCP server uses macros to determine
what network configuration information to send to a DHCP client.

When you configure the DHCP server, the management tools gather information
from system files and directly from you through prompts or command-line options
you specify. With this information, the management tools create the following
macros:

Network address macro, named to match the IP address of the
client network. The macro contains information needed by any client that is
part of the network, such as subnet mask, network broadcast address, default
router or router discovery token, and NIS/NIS+ domain and server if the server
uses NIS/NIS+. Other options applicable to your network might be included.

Locale macro, named Locale. The macro contains
the offset (in seconds) from Universal Time to specify the time zone.

Server macro, named to match the server's host name. The macro
contains information about the lease policy, time server, DNS domain, and
DNS server, and possibly other information that the configuration program
was able to obtain from system files. This macro includes the Locale macro.

The network address macro is automatically processed for all clients
located on that network. The locale macro is included in the server macro,
so it is processed when the server macro is processed.

When you configure IP addresses for the first network, you must select
a client configuration macro to be used for all DHCP clients using the addresses
you are configuring. By default, the server macro is selected because it is
contains information needed by all clients that use this server. Clients receive
the options contained in the network address macro before those in the server
macro. See Order of Macro Processing for more information about the
order in which macros are processed.

Dynamic and Permanent Lease Type

The lease type determines if the lease policy applies
to the addresses you are configuring. During initial server configuration,
DHCP Manager allows you to select either dynamic or permanent leases for the
addresses you are adding. If you configure with the dhcpconfig
command, leases are dynamic.

When an address has a dynamic lease, the DHCP server can manage the
address by allocating it to a client, extending the lease time, detecting
when it is no longer in use, and reclaiming it. When an address has a permanent
lease, the DHCP server can only allocate it to a client, after which the client
owns the address until the client explicitly releases it. When the address
is released, the server can assign it to another client. The address is not
subject to the lease policy as long as it is configured with a permanent lease
type.

When you configure a range of IP addresses, the lease type you select
applies to all the addresses in the range. To get the most benefit from DHCP,
you should use dynamic leases for most of the addresses. You can later modify
individual addresses to make them permanent if necessary, but the total number
of permanent leases should be kept to a minimum.

Reserved Addresses and Lease Type

Addresses can be reserved by manually assigning them
to particular clients. A reserved address can have a permanent or dynamic
lease associated with it. When a reserved address is assigned a permanent
lease:

The address can be allocated only to the client that is bound
to the address

The DHCP server cannot allocate the address to another client

The address cannot be reclaimed by the DHCP server

If a reserved address is assigned a dynamic lease, the address can be
allocated only to the client that is bound to the address, but the client
must track lease time and negotiate for a lease extension as if the address
were not reserved. This allows you to track when the client is using the address
by looking at the network table.

You cannot create reserved addresses for all the IP addresses during
the initial configuration because they are intended to be used sparingly for
individual addresses.